1. Technical Field
The embodiments herein generally relate to analog televisions, and, more particularly, to an oscillator architecture for an analog television receiver.
2. Description of the Related Art
Analog television encodes television picture and sound information and transmits it as an analog signal, in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal. All systems preceding digital television, such as NTSC, PAL, or SECAM are analog television systems. In color television systems for NTSC and PAL, color information is modulated with a color sub-carrier tone. In order to decode color information, one must first get synchronized with the color sub-carrier tone. A local color sub-carrier tone in the receiver must be reproduced with the same frequency and phase as the transmitted color sub-carrier tone.
In NTSC and PAL, besides the modulated color information, the TV signal also provides a color burst signal at the beginning of each line. In the receiver, one just needs to get synchronized to the color burst signal in order to correctly decode the color information. The device which performs the task of synchronization to the color burst signal is called a burst locked oscillator (BLO). FIG. 1 illustrates a traditional BLO architecture 100 having a phase detector 104, a low pass filter (LPF) 106, a burst accumulator 108, a BLO controller 110, and a digital voltage controlled oscillator (VCO) 112. The input signal to the BLO 100 is a composite video signal (Color, Video, Blank, and Sync (CVBS)), as well as a burst gate signal from a horizontal and vertical synchronization (HV SYNC) block 102.
The BLO 100 locks to, gets synchronized with, or recovers the reference color sub-carrier tone which is transmitted during the color burst of each line. Then, the recovered color sub-carrier tone mixes down with the received modulated color information. The mixed down color information is finally sent to the LPF 106 to recover the color information. In the traditional BLO 100, it is hard to have good color lock under mobile and noisy conditions at the same time. Thus, there is a need for an improved burst locked oscillator architecture for analog television.